The present invention relates to a system in which outer lifting cords are eliminated from blinds or shades. More specifically, the present invention relates to window covering systems which employ one or springs to balance the weight of window covering material and to accumulate the lifting cord within the head rail and/or bottom rail as the blind or shade is raised or lowered.
Venetian blinds have known for many years and typically include a plurality of slats made from metal, plastic, wood or other materials and supported by ladders. FIG. 1 shows a conventional venetian blind system 10 that includes a plurality of slats 12 located between a head rail 14 and a bottom rail 16. Prior art blind system 10 typically include a tilt mechanism 18 so that slats 12 can be moved from a horizontal position to a nearly vertical position to control the amount of light passing therethrough. As also conventional, blind system 10 includes lifting cords 20 and 22 which are coupled to the bottom rail, pass upwardly through the slats and into mechanisms within the head rail 14, and terminate in an exposed cord loop 24 outside the blind or shade. The lifting cord is so exposed to facilitate pulling of the outer pull cord 24 by hand, which in turn raises or lowers the bottom rail and any accumulated slats. Because of the natural tendency of the bottom rail and accumulated slats to free fall, locking mechanisms 25 are also commonly employed with such prior art blind systems.
Similar lift cord systems are used in a variety of the xe2x80x9csoftxe2x80x9d window products which are currently popular, including window coverings having pleated fabric between the head rail and the bottom rail, window coverings which have cellular fabric material between the head rail and the bottom rail, light control products which include cells having opaque portions arranged between the bottom rail and the head rail for light control and the like.
Systems are also known wherein the lift cords do not exit the head rail at all. Such systems are shown in Kuhar U.S. Pat. No. 6,234,236, issued May 22, 2001, U.S. Pat. No. 6,079,471, issued Jun. 27, 2000, U.S. Pat. No. 5,531,257, issued Jul. 2, 1996, and U.S. Pat. No. 5,482,100, issued Jan. 9, 1996. These systems use spring motors to balance the weight of the bottom rail and accumulating window covering material as the window covering is raised or lowered by simply grasping the bottom rail and urging it upwardly or downwardly.
Other patents show various spring devices used with venetian blinds. For example, in Cohn""s U.S. Pat. No. 2,390,826, issued Dec. 11, 1945 for xe2x80x9cCordless Venetian Blinds,xe2x80x9d two coil springs are used to provide even force, with a centrifugal pawl stop. The blind is raised by freeing the pawl to allow the spring to provide a lift assist. Other more conventional systems employing springs and ratchet and pawl mechanisms include those shown in Etten""s U.S. Pat. No. 2,824,608, issued Feb. 25, 1958 for xe2x80x9cVenetian Blindxe2x80x9d; U.S. Pat. No. 2,266,160, issued Dec. 16, 1941 to Burns for xe2x80x9cSpring Actuated Blindxe2x80x9d; and U.S. Pat. No. 2,276,716, issued Mar. 17, 1942 to Cardona for xe2x80x9cVenetian Blind.xe2x80x9d
It would be desirable to provide a cordless window covering system with an inexpensive and simple cordless mechanism.
The present invention features a cordless blind system which employs one or more linearly shaped springs (i.e., an extension or compression spring) to balance the weight of window covering material and to accumulate the lifting cord within the head rail and/or bottom rail. The present invention further features a system which is easy to adapt to a wide variety of blind designs and sizes and has the capability of applying spring forces in a variety of ways and combinations.
According to a first aspect of the present invention, a window covering system comprises a plurality of slats located between a head rail and a bottom rail. The bottom rail is connected to the head rail by at least one lifting cord. At least one first biasing devices is located in one of the head rail and the bottom rail. The at least one first biasing devices has a fixed end and a free end that is free to move in a direction along an axis of the head rail or bottom rail. The at least one lifting cord is operatively connected to the free end of the at least one of the first biasing device so that movement of the bottom rail causes a corresponding movement in the free end of the first biasing device in the direction of the axis of the head rail or bottom rail.
According to another aspect of the present invention, a window covering system comprises a plurality of slats located between a head rail and a bottom rail. The bottom rail is connected to the head rail by at least two lifting cords extending through the slats. A pair of first linear springs is located in one of the head rail and the bottom rail. The first linear springs has first ends anchored to an inner surface of the head rail or the bottom rail and second ends that are free to move within the head rail or the bottom rail. At least one of the lifting cords is operatively connected to the free end of at least one of the linear springs so that movement of the bottom rail causes a corresponding movement in the second end of the linear spring.
According to another aspect of the present invention, a window covering system comprises a plurality of slats located between a head rail and a bottom rail. The bottom rail is connected to the head rail by at least two lifting cords extending through the slats. A first spring motor and storage device is located in one of the head rail and the bottom rail. The first spring motor and storage device includes a linear spring having one end that is fixedly secured in the head rail or bottom rail and a second end that is free to move within the head rail or bottom rail. At least one of the lifting cords is operatively connected to the free end of at least one of the coil springs so that movement of the bottom rail causes a corresponding movement in the second end of the coil spring.
According to a further aspect of the present invention, a method for balancing a window covering system includes operatively connecting a fixed end of a linearly shaped spring to a non-movable anchor in a hear rail or bottom rail so that the fixed end remains stationary, an opposite free end of the linearly shaped spring being free to move toward and away from the fixed end. The method further includes operatively connecting the at least one lifting cord to the free end of the linear shaped spring so that movement of the bottom rail in a vertical direction causes a corresponding movement in the free end of the linearly shaped spring in a direction along an axis of the head rail or bottom rail.
These and other benefits and features of the invention will be apparent upon consideration of the following detailed description of preferred embodiments thereof, presented in connection with the following drawings in which like reference numerals are used to identify like elements throughout.